Natural gas streams produced from some subterranean formations frequently contain substantial volumes of various acid gas fractions such as hydrogen sulphide (H2S), carbon dioxide (CO2) and the like. The natural gas, commonly referred to as “sour gas”, must be purified and the acid gas fractions removed before being sent to market. The process of removal of these acid gas fractions is referred to in the industry as “sweetening” the sour natural gas stream.
There are various methods for sweetening sour gas to remove acid gas fractions therefrom. One of the most common methods has been to recover those acid gas fractions from the natural gas stream and to process it in a plant to produce elemental sulphur or, alternatively, inject it into well spaces below the ground. Such practices are very expensive with almost no monetary returns or gains. Beyond the cost associated with this type of method, there are negative environmental impacts on a number of levels.
The safe handling of sour gas and the removal of acid gas fractions therefrom is a significant economic factor in the feasibility of certain hydrocarbon recovery projects. In cases where it has been desired in the past to remove hydrogen sulphide and other acid gas fractions from a natural gas stream for example, solvent absorption methods have been practiced in the past whereby the gas stream from the well site is conveyed to a central processing facility where the hydrogen sulphide or other identified non-desirable acid gas fractions are removed by solvent absorption or other similar techniques.
Another source of by-product H2S is from the gasification of coal. Gasification is a process by which coal or other low-value carbonaceous solid fuels are gasified in a large chemical reactor. The resulting synthesis gas (syngas) comprises mostly hydrogen and carbon monoxide, and conventionally is cleansed and then used to fire an electric power plant. Syngas may also be converted into high value products such as synthetic fuels or ammonia. Several by-product streams are generated during gasification, including a stream of hydrogen sulphide gas.
There has been little effort made to produce an economically valuable product from by-product hydrogen sulphide gas. Sulphuric acid is one such valuable product that could be further produced from hydrogen sulphide that is recovered from acid gas waste streams of hydrocarbon processing. Several commercially established techniques are available in the market to convert hydrogen sulphide gas to sulphuric acid. However the production of sulphuric acid from hydrogen sulphide is commercially limited due over production consequently resulting in low market price.
Some work has been done relating to conversion of sulphur dioxide (SO2), such as from flue gasses in coal powered electricity generation, to sulphuric acid. There have also been efforts in developing processes for conversion of hydrogen sulphide (H2S) to sulphuric acid by treatment with hydrogen peroxide, sodium sulphates and ferric sulphates, however these have proven to be costly and difficult to implement on a large, industrial scale. It is therefore desirable to find an economic and safe method of converting otherwise waste acid gas streams to valuable sulphuric acid, which can then further be used to produce fertilizer.